Meteorology forAirborne Scientists

Henry FuelbergDepartment of Meteorology

Florida State University

Atmospheric Structureand Thermodynamics

Some Basics

Basic Atmospheric Variables

• Pressure (p)• Temperature (T in oC or K)• Density (ρ) ( or specific volume (α = 1/density))

(kg m-3)• Water vapor content• Three dimensional wind

Atmospheric Pressure Changes with Altitude

Pressure = Force/Area

1 Pascal = 1 Newton m-2

1 millibar (mb) =

1 hectoPascal (hPa)

Mean sea level pressure =

1013.25 mb

Mean sea level density =

1.25 kg m-3

Thermal Structureof the Atmosphere

Lapse rate = - ∂T/∂z

Troposphere has + lapse

Stratosphere first isothermal, then – lapse

Troposphere has small scale inversions that vary daily

Height of the TropopauseVaries with Latitude

ThermodynamicsParcel = imaginary volume of air to study, like a balloon, separate from environmentAtmosphere acts as an ideal gas—a mixtureEquation of state (ideal gas law)

Press = density x gas constant x temp

gas const = weighted by composition and molecular weight

First Law of Thermodynamics

• dq = cv dT + pdα heat change = internal energy change + work done to expand or contract vol.

• dq = cp dT – α dp heat change = enthalpy change + …….

Dry Adiabatic Process• Consider an unsaturated parcel• dq = 0• 0 = cp dT – α dp• Parcels still can change temperature due to expansion and

contraction• Example—parcel expands, expends energy, T becomes cooler• Make substitutions and solve for dT/dz• dT/dz = -g/cp = 9.8 oC/km = Γd (dry adiabatic lapse rate)• Unsat. parcels always follow Γd • Away from clouds and radiative processes, parcels ~ adiabatic

for several days

Rising air cools

Potential Temperature (θ)Parcel at T and pΘ is temp. parcel would have if taken dry adiabatically to p = 1000 mbIf p = 1000 mb, Θ = TΘ = T (1000 mb/ p) R/cp R/cp = 0.286 Parcels conserve Θ during ascent, descent, etc. as

long as conditions are adiabatic T is not conserved, it changes at ΓdHow does θ vary in previous figure?Therefore, Θ can serve as a tracer for parcels

Water Vapor

• Vapor pressure = partial pressure of vapor (mb)• Mixing ratio = mass vapor/mass dry air (g/kg)• Concept of saturation• Dew point temperature = temp to which air must

be cooled to become saturated (oC)• Relative humidity = mixing ratio / sat. mixing ratio

Saturated Adiabatic Process

• Parcel is saturated• Lift parcel, condensation occurs, latent heat

released, dq ≠ 0• dq = cp dT – α dp• Let dq = latent heat release• Perform some magic• Γs = Γd [ ≤ 1]• Therefore……….. Γs ≤ Γd not a constant• Γs ≈ 5-6 oC/km

Radiosondes

Hydrostatic StabilityDisplace parcel upward (could go downward)Will displacement be

Suppressed = Stable Layered clouds, steady precipitation Enhanced = Unstable Towering clouds, showers or Tstorms Neither = Neutral Parcel moves only to where pushed

Absolute StabilityEnvironmental Lapse Rate less than Wet Adiabatic Rate

Absolute InstabilityEnvironmental Lapse Rate greater than Dry Adiabatic Rate

Conditional InstabilityEnvironmental Lapse Rate between the Dry and Wet Adiabatic Rates

What Causes Wind to Blow ??

It is acted on by forces—most of which we can’t see

Surface Map Isobars = Lines of constant pressure

Straight Isobars

Flow Around Circular Low

Flow Around Circular High

Upper Level ChartsPressure is Vertical Coordinate

500 mb Chart

Planetary Boundary Layer (PBL)• Lowest layer of atmos—directly influenced by the

surface• PBL vs. Free Atmosphere• What happens in PBL?• Air is heated/cooled from below—radiation• Inversions (stable) at night—suppress mixing• Big lapse rate during day—less stable-lots of mixing• Mechanical Turbulence—roughness (day or night)• Thermal Turbulence—thermals (day)• You can bounce around a lot!!

• Wind Speed goes to zero at surface (no slip)• Speed increases with height according to Ekman

Theory—direction also changes• The more mixing• the more θ is constant with height• the more mixing ratio constant with height• Height of PBL deep during day, shallow at night • Depth determined by– Temperature– Wind Speed– Others

Transporting Air From Surface to Higher Levels

Winds are stronger thereWind direction often changes with height

Jet Streams

Middle Latitude Wave Cyclones

Major Airstreams in Midlat Cyclone

Smaller Scale CirculationsAlso Provide Vertical Transport

Sea/Land Breezes

Mountain/Valley Breezes

Santa Ana Winds & Fires

Wires Fanned by Santa Ana Winds

Thunderstorms-Major Vertical Transporters

Lightning Creates NOx

FOG

Radiation Fog

Advection Fog

Yesterday’s Fog (4:46 PM)

This morning

Neat PictureContrails Cover 0.1% of Earth’s Surface

Eastern France

TrajectoriesBackward in time—where did air come from? What path did it take?Forward in time—where is air going to?

What path will it take?Several possible procedures

Isobaric—air keeps same pressure--move parcel by horizontal winds

Isentropic—air follows θ surface—move air by winds on the θ surface

• Kinematic method—move parcels by three-dimensional winds—most popular today

Procedure for Forward TrajectoriesStart with 4-D grid of 3-D wind

components—hope data every few hoursMove parcel one time step by these windsNow at a new location and a new time

• Take winds at new location and time and move parcel another time step

• Repeat the process until you reach theending time that you specify

• Limit is usually 5-10 days• After that uncertainties are too great

• If backward trajectories, process goes in reverse

Examples from ARCTAS-200810 days back from selected flight legs

Heading to N CA

Heading to S CA

Particle Dispersion Models•Establish locations of emissions and rates of emission•Release particles to simulate emission rate•Particles have specified mass and are released at specified rate•Three-dimensional winds move the particles•Can then watch the transport of the emissions

WRF Nested Grid 45 km, 15 km, 5 km

Spring

Summer

Sources of Real Time Information

Satellite, Radar, Surface Analyses,Upper Air Analyses, Forecasts

http://www.rap.ucar.edu/weather/

Surface Plot 7 PM

Edward AFB Radar 8 PM

Enhanced IR Image 8 PM

Surface Plot 11 AM

Visible Images 10 AM

Edwards AFB Monday 5 AM

500 mb Analysis 5 AM Monday

Forecast Products

NOAA National Center for Environmental Prediction

http://www.nco.ncep.noaa.gov

We look at 54 h progs valid11 AM Wednesday

SFC Forecast

H

Clouds below 6000 ft

850 mb Forecast

700 mb Forecast

500 mb Forecast500 mb

Zoom to CA Area

300 mb Forecast

Your Local NWS Office

http://www.srh.noaa.gov

Other Interesting Sites

Storm Prediction Center http://www.spc.noaa.gov

National Hurricane Center http://www.nhc.noaa.gov